420 PROCEEDINGS OF THE ACADEMY OF 



large arched opening beneath the umbo. This truncation makes but a small 

 angle with the miduinbonal slope, the arch beneath which is partly closed by 

 the curtain-like deflection of the posterior part of the shell. External surface 

 marked by fine radiating ribs, and a few concentric rugae in front of the beak 

 and along the anterior terminal expansion. 



Height of shell from beak along midumbonal slope to remotest point of 

 ventral border *59 (100); distance from anterior cardinal angle across the shell 

 at right angles with posterior truncation -42 (71); convexity of right valve 

 15 (25). 



Localities. Marshall, Battle Creek, and R. R. Cut, 3 miles North of Napo- 

 leon, Jackson county. 



Conocardium, Bronn. 



Coxocaedium ? bovipedale, n. sp. Shell small, very ventricose, truncated 

 along the umbonal slope, or a little posterior thereto, by a plane nearly verti- 

 cal to the plane of the valves, but a little inclined posteriorly, thus producing 

 a slightly acute plane angle with the external surface. Beak prominent, 

 somewhat enrolled and turned forward ; hinge-line anterior, short, convex, 

 joining, by a rounded, obtuse angle, the gently rounded anterior angle, which 

 curves more rapidly in approaching the ventral margin and the truncation. 

 Posterior, truncated side nearly flat, but a little concave, with an arched, 

 mactra-shaped opening under the umbo. Convex surface of shell, with 26 

 radiating ribs, slightly flattened along their summits, and very fine, sharp, 

 undulating, concentric etriae, most distinct between the anterior angle and 

 the umbo ; the truncated surface with obsolete arched striae. Right valve 

 unknown. 



Length along truncating line *30 (100); distance from anterior extremity to 

 truncating plane, at right angles with latter - 20 (67); convexity of left valve 

 12 (40). 



Locality. Marshall. 



This species belongs to the group of C. Napohonense, but may be easily dis- 

 tinguished by its coarser ribs, greater ventricosity, less flattened marginal 

 regions and nearly mesial truncation. 



Posidonomya, Brown. 



Posidoxomya RoMiNGEEi, n. sp. Shell of medium size ; general outline about 

 two-thirds of an ellipse, the longer axis of which is nearly at right angles 

 with the anterior cardinal slope of the shell, and forms an angle of 75 with 

 the straight hinge-line, and one of 33 with the midumbonal slope ; greatest 

 width of shell a little nearer the (regularly curved) ventral border ; region 

 behind the beak a little excavated, making the posterior cardinal region 

 appear slightly flattened and produced ; beaks elevated above the hinge-line, 

 approximated and slightly turned forward. Surface (of cast) distinctly 

 marked by continuous equidistant and direct concentric striae. Hinge un- 

 known. 



Greatest length of shell (over midumbonal slope) - 97 (100); longer axis of 

 the elliptic outline '90 (92); greatest width of shell (at right angles with last 

 measure - 70 (72); thickness of right valve "20 (21); number of striae in one- 

 tenth of an inch, in the middle of the shell 3. 



Locality. Marshall. 



Closely imitates in outline P. vetusta, Sow. sp. (Phill. Geol. Yorks. 211, pi. 

 vi. 3), but the beak is less projecting, and the concentric furrows are more 

 numerous and smaller. 



Posidonomya Whtteana, n. sp. Shell of moderate size, oblique, with an 

 extended, straight, hinge-line, a subalate expansion before, and a rather flat- 

 tened and extended posterior margin. Beaks little elevated above the hinge, 

 incurved, and slightly turned forward. Umbonal ridge much swollen, situa- 

 ted anterior to the middle of the shell, and making an angle of 66 with the 



[Sept. 



